The present invention relates to electrophoresis cassettes made entirely of plastic materials.
Electrophoresis gels are widely used for separating and analyzing biomolecular materials such as proteins, DNA and DNA sequence, for example. A gel medium, such as agarose or acrylamide, is commonly held inside a thin, rectangular shaped cassette composed of two electrically-insulating, liquid impermeable sheets, such as glass plates, which are held in spaced apart, opposing relationship by insulating spacers or the like.
A liquid solution containing the medium is poured, pumped or pipetted into the space or gap created by the two plates in the cassette. A comb type device may be inserted into the cassette while the media is still in a liquid form. The agarose or acrylamide solutions are made to change into a gel either by cooling as in the case of agarose or via polymerization as in the case of acrylamide. The comb enables sample wells to form in the gel. The entire top of the gel may be used for separating sample, if a researcher chooses not to use a comb. After the comb is removed, samples can be loaded into each well for electrophoresis.
These cassettes are typically placed in an apparatus where electrical power is made to pass through the gel causing the biological sample to travel through the gel media. During travel of the sample material through the gel, the components of the sample separate from each other based upon principles of electrophoresis.
Originally, cassettes were made using two glass plates with a spacer material placed between the glass on each end in order to create the gap where the gel media is located. The glass plates were normally sealed on the bottom of the cassette using any of various means such as tape or silicone rubber gaskets, for example. These prior art designs, unfortunately, require extra labor and are costly to manufacture.
It has been proposed to make integral plastic cassettes that would reduce labor and material costs and which would be more economical to manufacture. However, attempts to make such plastic cassettes that are compatible with many of the existing electrophoresis apparatus have not proven altogether successful. One problem has been that in order to seal the bottom of the cassette gap without at the same time increasing the size of the cassette, it would be necessary to reduce the vertical height of the gel medium. Unfortunately, this limits the usefulness of the plastic cassette as compared to prior designs.
Another problem has been that plastic cassettes must be made thin enough to fit into existing apparatus. A front plate made of plastic is not as stiff as a glass plate of the same thickness and, consequently, thin plastic plates are more prone to excessive deflection. Deflection of the front plate can be detrimental to both the gel formation and operation.
Some prior art cassettes have been made utilizing a back plate made of plastic and a thin front plate made of glass in order to accommodate the limited space and to interface with and seal against the stepped upper tank buffer seal of some existing apparatus. These cassettes, nevertheless, utilize tape on the bottom and along the front plate of the cassette to seal the liquid contained in the gel during polymerization. The assembly of plastic and glass require additional labor and cost to manufacture.
Another prior art cassette has been made utilizing plastic front and back plates wherein a slot located on the back plate of the cassette exposes the lower portion of the gel. However, in order to employ the slot in cassettes for some existing electrophoresis apparatus, a portion of the gel length would have to be reduced. Furthermore, these slotted cassettes would require the use of tape to seal off the slots.
It is therefore an important object of the invention to provide an improved electrophoresis cassette which is made entirely of plastic material, which is economical to manufacture and which is compatible with electrophoresis apparatus currently in the field.
Another object of the invention is to provide an improved electrophoresis cassette which maintains nearly the same gel length as that produced in glass cassettes of the prior art and which are compatible with existing electrophoresis apparatus.
Still another object of the invention is to provide an improved electrophoresis cassette that will interface properly with the step type seal employed in existing electrophoresis apparatus.